Abstract: Joanna Barkas
Mentor: Dr. Davis
This summer we will be investigating polyphenisms, which are adaptive changes in phenotype in response to environmental cues. In particular, we will be studying the reproductive polyphenism in the pea aphid wherein females can be either asexual or sexual. Other than the need for males, an important difference between sexual and asexual females lies in their own means of producing offspring. The sexual females are oviparous, meaning that they lay eggs such that embryogenesis of their young occurs externally. In contrast, asexual females are viviparous, meaning that they give live birth and their offspring complete embryogenesis internally. We will be studying the differences in pattern formation during oogenesis and embryogenesis of viviparous versus oviparous aphids. We will focus on a patterning system, known as the terminal system that was first described in Drosophila. We have identified several genes involved in this pathway that appear to be differentially expressed during viviparous versus oviparous development. I will be refining our descriptions of these differences using in situ hybridization to visualize gene expression. In addition, a critical part of this investigation is the ability to functionally interfere with particular genes during either oviparous or viviparous development, potentially providing additional evidence for function differences in pattern formation. We will pursue the technique of RNA interference, which has been widely used to knock down gene function in a wide variety of non-genetic organisms. As a target for our first attempt, we will focus on the gene distal-less, which encodes a transcription factor required for the development of limbs. Working with Emma Hedman, I hope to knockdown distalless function in either asexual or sexual aphids, assaying for both phenotypic effects (i.e., loss of distal appendages) and loss of distalless mRNA (by in situ hybridization).